Frill-necked lizards are almost a metre (3.3 feet) long with colours ranging from green to dark orange. They are all the same species though; the colour varies to match the local vegetation. Frill-necked lizards have a fan of cartilage spines around their head, supporting a wide flap of skin. The spines are connected to the base of the tongue so, when the lizard gapes its mouth, the frill spreads wide. This is used to scare away predators and also for courtship signalling.

They are also the only lizards that can balance properly on two legs; other lizards can run on their hind legs but they fall forward as soon as they slow down.